Natural sources of pressure are typically utilized in the primary production of fluids from an oil reservoir. As a practical matter, pressure derived from: the evolution of dissolved gas from oil, gas cap expansion, and water encroachment comprise the three principal reservoir drive mechanisms. To a lesser extent, liquid expansion, reservoir compaction, and gravity also play a role in the production of hydrocarbon fluids. As a practical matter, however, most reservoirs produce fluids through some combination of each mechanism.
As is well known, at some time during the producing life of an oil reservoir, its internal pressure may be reduced to the point where supplemental energy is required to maintain production rates at economic levels. In the usual case, measured volumes of gas or water are delivered to the partially depleted reservoir through one or more wellbores provided for this purpose to increase the internal pressure of the reservoir as well as its productive life. This process commonly referred to as secondary recovery.
On average, primary and secondary recovery processes produce no more than approximately one-third of the "oil originally in place" (OOIP) in a given oil reservoir. To recover the remaining OOIP, various enhanced recovery techniques have been proposed. With the exception of steam flooding and in situ combustion, with their attendant pollution related drawbacks, most enhanced recovery techniques involve the injection of one or more chemical compositions into a targeted reservoir. Due to the relatively high costs associated with preparing and handling these chemical compositions, however, enhanced recovery projects will account for little oil recovery in the United States during the foreseeable future.
At the present time, nearly eighty percent of our domestic oil wells produce less than ten barrels of oil per day. This low rate of oil production is often due, in part, to the accumulation of oil bearing liquid in the well which imposes an additional backpressure on a pressure depleted reservoir further impeding liquid flow therein. In some wells, this liquid accumulation may altogether halt the further production of oil thus necessitating well abandonment. As the installation and operation of mechanical pumps to lift oil bearing liquid from a well is costly, a significant need exists, therefore, for an economical means for increasing oil recovery from marginally productive wells.